1. Field of the Invention
The present invention relates generally to an engine-starting air-to-fuel ratio control system and more specifically to an electronic control system incorporated with a carburetor including an actuator for increasing the amount of fuel supplied to an engine when th engine is started or being idled.
2. Description of the Prior Art
Recently, electrically or electronically controlled carburetors have been developed in order to improve engine starting characteristics when an engine is started or being idled, in particular, at low temperatures. In these carburetors, a starter nozzle is provided on the downstream side of a throttle valve to supply a rich mixture into an engine without installing a conventional choke valve. An example of these engine-starting air-to-fuel ratio control apparatus is disclosed in Japan Unexamined Patent Application No. 58-135347.
In this apparatus, a richer mixture supplying solenoid is installed in a passage communicating with the starter nozzle in order to increase the amount of fuel in starting an engine. In more detail, when an engine is started or being idled, the richer mixture supplying solenoid is activated to additionally supply fuel through the starter nozzle or to supply a rich mixture. Further, the increase in the amount of fuel is determined on the basis of detected engine speed, intake air pressure and engine coolant temperature.
In the prior-art engine-starting air-to-fuel ratio control apparatus as described above, however, because the amount of increase in fuel is controlled by only three factors (engine speed, intake air pressure and engine coolant temperature), the engine starting characteristics are subjected to change in outside air (intake air) temperature, thus resulting in a problem in that engine starting characteristics are not satisfactory. For instance, even if coolant temperature is at an appropriate value, when outside air temperature is low, fuel will not be evaporated stably and therefore air-to-fuel ratio increases (mixture becomes lean) as compared with when outside air temperature is high. As a result, the engine starting characteristics are deteriorated.
The arrangement of the prior-art engine-starting air-to-fuel ratio control apparatus will be described in greater detail hereinafter with reference to the attached drawing under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS.